Encapsulation of oils and fragrances by core-in-shell structures from silica particles, polymers and surfactants: The brick-and-mortar concept

Abstract

Colloidosomes provide a possibility to encapsulate oily substances in water in the form of core-in-shell structures. In this study, we produced microcapsules with shell from colloidal particles, where the interparticle openings are blocked by mixed layers from polymer and surfactant that prevent the leakage of cargo molecules. In other words, the particles and polymer play the role of bricks and mortar. For this goal, we used hydrophilic silica particles, which were partially hydrophobized by the adsorption of potassium oleate to enable them to stabilize Pickering emulsions. Various polymers were tested to select the most appropriate one. The procedure of encapsulation is simple and includes single homogenization by ultrasound. The produced capsules are pH responsive. They are stable in aqueous phase of pH in the range 3 -6, but at pH > 6 they are destabilized and their cargo is released. With the optimized formulation of silica particles, polymer, oleate and NaCl, we were able to encapsulate various oils and fragrances, such as tetradecane, limonene, benzyl salicylate and citronellol. All of them have a limited and not too high solubility in water. In contrast, no stable microcapsules were obtained with oils that either have zero water solubility (mineral and silicone oil) or higher water solubility (phenoxyethanol and benzyl alcohol). By analysis of results from additional interfacial-tension and thin-film experiments, we concluded that a key factor for obtaining stable capsules is the irreversible adsorption of the polymer at the oil/water interface. The hydrophobization of the particles by surfactant adsorption (instead of silanization) plays an important role for the pH responsiveness of the produced capsules. The obtained information about the role of various factors for the stabilization of microcapsules, which are based on the brick-and-mortar concept, can be further used to achieve better stability; selection of polymers that are appropriate for different classes of oils, as well as for the production of smaller capsules stabilized by nanoparticles. (P.A. Kralchevsky). Introduction.The development of micro-and nanocapsules with controlled composition and properties has been a subject of intensive research in the last decade. The stimuli responsive release of cargo molecules from the carrier gains a remarkable attention for in vivo and in vitro delivery of contrast agents, genes, and pharmaceuticals [1]. The colloidal capsules find another broad field of applications in house-hold and personal-care detergency, cosmetics and food industry, e.g. for the encapsulation of fragrances, flavors, colorants and preservatives [2,3].By their chemical nature, the colloidal carriers are classified as inorganic, organic and hybrid, e.g. mineralized protein capsules [1,4]. Different classes of colloidal carriers can be distinguished in relation to their structure and morphology: micelles; dendrimers; liposomes; niosomes; polymersomes; cubosomes and hexosomes; colloidosomes, and emulsion-based micro-and nanocapsules [1,5...

Cross-linking of double oil-in-water-in-oil emulsions: A new way for fragrance encapsulation with tunable sustained release

“…Alternatively, the pressure could be released and the liquid remaining outside analyzed by GC ( Figure 20 The comparison of the proposed capsules with all the existing ones without focus on the goal and application is just an impossible task in the frame of an original paper. Therefore, the ambitious of this paragraph is limited to a comparison with some recent and novel systems [19,20,23,39,40,[52][53][54][55][56][57][58][59][60][61][62][63]] that aims at reducing or avoiding the use of formaldehyde, most of them being core-shell capsules. Also depending on the considered application, either a provoked sudden release of the cargo is aimed at [19,20,[54][55][56][60][61][62] or, on the contrary, a slow and sustained released is preferred or observed as it was the goal herein [39,40,52].…”

“…Pickering emulsions that is to say emulsions stabilized by particles are known to be very stable kinetically. In order to improve their tightness or mechanical properties the emulsion surface may be reinforce either by polymers that serve as a mortar [55], by polymerization at the interface [57] or by in-situ synthesis of a silica shell [19,20,54,[60][61][62][63][64][65].…”

“…One could discuss whether these Pickering-based capsules belongs to the new class of the so-called colloidosomes [55,66] that are shell-like capsules formed by the self-assembly of colloidal particles at the interface of emulsion droplets. The term "colloidosome" has been proposed by Dinsmore and co-workers [67] and designates such drops covered by colloidal particles with a second step consisting in the particle locking at the interface and a possible third step where capsules are transferred by centrifugation into a solvent that is typically the same as the internal phase.…”

Formulation, Stability and Physicochemical Properties of Pickering Emulsions: An Overview

“…Two properties of Pickering emulsions appear to be particularly interesting, the very good stability and the specific interfacial properties. The assembly of nanoparticles with fluid interfaces, as is the case with the stabilization of Pickering emulsions, is a method of forming a shell around droplets (Radulova et al, 2018). This type of structure corresponds to encapsulation systems which have the advantages of: encapsulating and protecting labile active principles against degradation by an unfavorable pH medium or by enzymes of the digestive fluids (Marefati et al, 2017;Shao et al, 2018;, modulating the important fundamental biological process of lipid digestion by virtue of their distinctive stability against coalescence and resilience to desorption by intestinal biosurfactants (Sarkar et al, 2018).…”

A novel photothermo-responsive nanocarrier for the controlled release of low-volatile fragrances

“…Over the last decade, the development of avor and fragrance nanocapsules has drawn extensive attention in academia and industry. [9][10][11][12][13] In this regard, porous silica-based materials are particularly attractive as a matrix for encapsulation of fragrant molecules, [14][15][16][17][18][19] because they offer inherent advantages over the commonly used polymers, such as high mechanical resistance, excellent biocompatibility, and great loading capacity. 14 For example, Zhu et al employed mesoporous silica nanoparticles (MSNs) modied with polyelectrolytes to enclose hydrophilic perfume, which improved the loading content of fragrance and long-lasting effects.…”